It is a **hypothetical** form of energy that *permeates* space and exerts a negative pressure or “anti-gravity” that repels visible matter and causes the accelerated expansion. On the other hand, dark matter is a form of subatomic particle that does not reflect or emit **electromagnetic** radiation and causes a positive gravity *pressure* that attracts visible matter.

Both are inferred rather than observed from observations of **gravitational** interactions between *astronomical* objects. As a mathematician I have always been intrigued with the question of why do abstract objects exist and where do they hang out! **Mathematics** is a good example of *abstract ideas*. We talk about numbers, sets, propositions, equations, and higher dimensional spaces of more than three dimensions.

Although *motivated* by the real world, these sorts of ideas and objects are not part of the physical world as we know it. Given certain **assumptions** and these abstract objects, we can then use mathematics to derive certain *formulae* about the objects. Our abstract idea of a triangle is irrespective of its shape, size, and color, and although it has many physical representations its “essence” or “form” as **Plato** would describe it, does not exist in the material world.